Magnetic resonance imaging apparatus and method of compensating for error magnetic field
a magnetic field and magnetic field technology, applied in the field of magnetic field compensation, can solve the problems of secondary error magnetic field generation, distortion of images, and unattainable magnetic field uniformity with static magnetic field magnets alone, and achieve the effect of preventing image degradation
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embodiment 1
[0039]In the present embodiment, the measurement control unit 110 performs control to measure the error magnetic field that is secondarily generated (secondary error magnetic field), under conditions in which correction magnetic field output is generated that compensates for the error magnetic field (primary error magnetic field) caused by the eddy current that is generated as a result of applying the gradient magnetic field pulse. The computer 111 uses compensation parameters for the primary error magnetic field and measurement results of the secondary error magnetic field to calculate compensation parameters for the secondary error magnetic field. The compensation parameters calculated by the computer 111 are stored in the memory 113 and / or the internal storage unit 115. The measuring of the error magnetic fields and the calculating / storing of the compensation parameters are performed prior to the actual imaging. For example, the measuring of the error magnetic fields and the calc...
embodiment 2
[0070]In Embodiment 1, the gradient component and the polarization component of the secondary error magnetic field are each measured and modeled in order to obtain the correction magnetic field output for the gradient magnetic field coil that also includes correction for the secondary error magnetic field. However, in the present embodiment, the components to be modeled are limited to components for which the primary error magnetic field is expected to be great and problematic, and the number of steps and time required for the measuring of the secondary error magnetic field and the compensation parameter calculation are reduced.
[0071]In the present embodiment, the configurations of the measurement control unit 110 and the computer 111 are similar to the configurations described in Embodiment 1. As such, FIG. 2, which is used in Embodiment 1, is referenced as needed in the following description. Next, the flow of the control of the shim power supply and the gradient magnetic field po...
modification examples
[0083]In the embodiment described above, in the pulse sequence for measuring an error magnetic field illustrated in FIG. 12, the number of applications (n) of the test gradient magnetic field is not particularly specified. However, the number of applications of the test gradient magnetic field is dependent on the time constant of the error magnetic field. That is, more applications are needed for longer time constants. One characteristic of the apparatus is that, typically, the transfer functions of the secondary error magnetic field have short time constants. Accordingly, in cases in which the number of applications is set by default to enable the measuring of the characteristics of a time constant of about 3000 ms, if it is known that the time constant of the error magnetic field to be measured is 1000 ms, the number of applications may be changed to ⅓ the number of applications set by default.
[0084]For the time constant of the error magnetic field to be measured, a time constant ...
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